1. Field of the Invention
The present invention generally relates to a presser foot system for sewing machine comprising a small tubular cylinder bed which is used, for example, in joining crotch sewing of underpants or drawers and joining shoulder sewing of shirts. More particularly, the invention relates to a presser foot system mounded on an interlock stitch sewing machine with which the upper edges of the ends of two fabrics to be fed in a vertical face-to-face contact are cut to an even length, and the resulting ends of the fabrics are stacked one on another on a stitch plate and then fed to a needle location for sewing the overlap portions.
2. Description of the Prior Art
When performing a sewing operation wherein the ends of two fabrics cut to a predetermined shape being stacked over a predetermined width are fed to a needle location while sewing the overlap portions, it is necessary to adjust the overlap width of the ends of the fabrics. If the sewing operator performs such adjustment by hand at a location, in the direction of sewing, before a presser foot system in which the fabrics are held and pressed against the stitch plate, a lot of labor and skill are required, resulting in poor operating efficiency. Further, difference in the degree of skill may often cause variations in the finished sewing article.
In order to omit such manual adjustment of the overlap width of two fabrics, that is, to perform such adjustment automatically, a presser foot system for sewing machine has conventionally been proposed and put into practice which has a specific construction and comprises a knife trimming mechanism and a guide means. The knife trimming mechanism cuts the edges of fabrics to be sewed into an even length, and the guide means guides the ends of the fabrics respectively to travel (move) to a needle location in order that these ends cut by the knife trimming mechanism are stacked one on another at a location before the needle location.
FIGS. 7 and 8 illustrate one particular example of known presser foot systems for sewing machine having a specific construction which comprises the above-mentioned knife trimming mechanism and guide means. Specifically, FIG. 7 is a perspective view of the vicinity of a needle location in an interlock stitch sewing machine. A sewing machine arm 1 has at its tip a needle bar (not shown) and a presser bar 2 that are aligned before and after in the sewing direction X and are supported vertically and downwardly. A number of needles 4 are attached via a needle clamp body 3 to the lower end of the needle bar. A presser foot system for sewing machine 5 is fixedly supported to the lower end of the presser bar 2.
The presser foot system 5 comprises (i) a pair of right and left presser feet 51 and 52, as shown in FIG. 8, which are disposed before a needle location 8 of a throat plate 7 fixed on the upper surface of a small tubular cylinder bed 6, so as to be free to make a flexible contact with the throat plate 7, (ii) a fabric guide path 9 that is formed between the opposed surfaces of the presser feet 51, 52 and is opened forward of the sewing direction X, (iii) a knife trimming mechanism 10 disposed in the course of the fabric guide path 9, by which the edge portions of the ends of right and left fabrics BR and BL in a vertical face-to-face contact are fed to the fabric guide path 9, and (iv) a guide means comprising upper and lower guides 11 and 12 which respectively guide the fabrics BR and BL cut to an even length by the knife trimming mechanism 10 to move to the needle location 8, thereby stacking the ends of the fabrics BR and BL.
The knife trimming mechanism 10 is made up of a fixed knife 10A and a movable knife 10B. The fixed knife 10A is fixed to one presser foot 51 with its cutting edge 10a1 (see FIG. 9) faced into the fabric guide path 9. The movable knife 10B is disposed on the side of the other presser foot 52 with its cutting edge 10b1 (see FIG. 9) faced into the fabric guide path 9. As shown in FIG. 7, the movable knife 10B is urged on its base end downwardly by a coil spring 14 and attached to the lower end of a rod 13 moving with the rotation of a main shaft (not shown) of the sewing machine, and is constructed so as to be free to rock in the directions indicated by arrows a and b crossing the fabric guide path 9. Thereby, the movable knife 10B is brought into a sliding contact in the plane horizontal to the upper surface of the fixed knife 10A by the action of the coil spring 14 that is generated by movement of the rod 13. As shown in FIG. 9, a contact guide piece 10b2 for guiding the sliding contact of the knives 10A and 10B is formed at one end of the movable knife 10B in the sewing direction.
The upper surface of the presser foot system 5 is provided with a guide slot 15 that extends from the terminal part of the fabric guide path 9 to an oblique rearward of the sewing direction X, so as to be continuous with the outer edge of the presser foot 51. By the guide slot 15, the ends of the fabrics cut by the knife trimming mechanism 10 are guided to the outside of the presser foot 51 and then discharged, without reaching the needle location 8.
The upper guide 11 of the guide means is disposed above the presser foot 52 and overhangs at its middle part toward the fabric guide path 9. As the upper guide 11 approaches the needle location 8, the amount of overhang toward the fabric guide path 9 is increased so as to be continuous with the upper guide slot 15. The lower guide 12 is disposed under the presser foot 51 and the amount of overhang toward the fabric guide path 9 is increased as it approaches the needle location 8, like the upper guide 11. Also, the lower guide 12 is formed so as to be substantially horizontally opposed to the stitch plate 7 with a predetermined gap therebetween.
In the presser foot system 5, slide plates 16 and 17 are attached to the lower surface of the paired presser feet 51 and 52, respectively, over the entire length in the sewing direction X. The slide plates 16 and 17 ensure slide between the fabrics BR and BL held and urged against the stitch plate 7, thereby facilitating the fabric feed operation of feed dogs (not shown). The lower guide 12 is integrally formed with the slide plate 16 on the side of the presser foot 51.
Operation to cut the ends of fabrics to an even length and to stack one on another performed by the presser foot system 5 so constructed will be described by referring to FIGS. 10A to 10E.
As shown in FIG. 10A, right and left fabrics BR and BL are fed to the fabric guide path 9 in such a state that their ends BRa and BLa having a predetermined width are stacked one on another. At this time, an auxiliary bar 18 may be used to hold the vertical state of the overlap portions of the fabrics BR and BL.
As shown in FIG. 10B, when the fabrics BR and BL fed in this state into the fabric guide path 9 reach the knife trimming mechanism 10, the movable knife 10B rocks in a direction to cross the fabric guide path 9 such that it is brought into sliding contact with the upper surface of the fixed knife 10A within a horizontal plane. Thereby, the upper edges of the ends of the fabrics BR and BL are cut to an even length. In this cutting position, the upper and lower guides 11 and 12 overhang in a predetermined amount within the fabric guide path 9. The end face of the upper guide 11 is in contact with the outer surface of the end of the resulting right fabric BR, and the end face of the lower guide 12 is in contact with the outer surface of the end of the resulting left fabric BL.
As shown in FIGS. 10C and 10D, as the left fabric BL of which upper edge is cut by the knife trimming mechanism 10 is fed in the sewing direction X, it is brought down to the stitch plate 7 when it is pushed from the left by the lower guide 12 in which the amount of overhang is increased as it approaches the needle location 8. On the other hand, the right fabric BR is pushed from the right by the upper guide 11 and is guided between the upper guide 11 and the underlying lower guide 12. Then it reaches the terminal end of the lower guide 12 and overlies the end of the left fabric BL lying on the stitch plate 7. The right and left fabrics BR and BL in such a stacked state are fed to the needle location 8 and the overlap portions are sewed by the needle 4 going down to the needle location 8, as shown in FIG. 10E.
In the conventional presser foot system for sewing machine comprising the above-mentioned knife trimming mechanism and guide means and performing the above-mentioned sewing operation, distance L1 from the center of the needle location 8 to the front end of the fixed knife 10A of the knife trimming mechanism 10 in the sewing direction X, namely to the position from which the knife trimming mechanism 10 starts to cut the fabrics to an even length, is set to 16.0 mm in actual dimension, as shown in FIG. 8. In FIG. 11, CW denotes one cutting width obtained by the knife trimming mechanism 10 that operates one time for each stitch motion of the needle 4 (i.e., one up and down motion), and H denotes the height from the upper surface of the stitch plate 7 to the cutting position (i.e., the lower surface of the fixed knife 10A). The distance L1 is set according to distance L needed in bringing down the ends of fabrics. The distance L is calculated by trigonometric function from the known values of the cutting width CW and height H, in order that the ends of the right and left fabrics BR and BL cut in a vertical state to an even length are stacked one on another on the stitch plate 7 until these reach the needle location 8.
However, the cutting width CW obtained by the knife trimming mechanism 10 varies depending on the thickness and flexibility of the fabric material. There is also height H variation because due to manufacturing tolerance inherent in each sewing machine, some difference in altitude may occur in the setting position of the fixed knife 10A and movable knife 10B of the knife trimming mechanism 10. In particular, when performing joining crotch sewing of underpants or drawers, a thick stage D is present at the initiation and termination of sewing, as shown in FIG. 12. Therefore, the cutting width CW and height H are smaller than that in other portions, and such cutting width CW and height H variations may cause the event that the ends of the right and left fabrics BR and BL cut to an even length cannot be brought down completely within the distance L set in the above manner.
Thus, in the conventional presser foot system for sewing machine in which the distance from the center of the needle location 8 to the cutting position of the knife trimming mechanism 10 is set to L1 (16.0 mm in actual dimension), there are the following problems. That is, if the ends of the right and left fabrics BR and BL are brought down incompletely, the ends of the fabrics BR and BL cut to an even length cannot be stacked in a predetermined state and fed to the needle location 8 for sewing. As a result, a seam C includes a projected portion C1 toward a seam direction Y (which is reverse of the sewing direction X) formed at the stage D of the initiation and termination of sewing, as shown in FIG. 12. This results in poor finish of the sewing article.
In addition, when the cutting quality of the knife trimming mechanism 10 is lowered for a long-term use, the cutting width CW may vary to cause such poor finish as above described, even if the thickness and flexibility of the fabric material are the same.
It is therefore an object of the present invention to overcome the foregoing drawbacks by providing a presser foot system for sewing machine in which the ends of two fabrics cut to an even length are fed in a predetermined stacked state to a needle location thereby sewing is always performed with high quality finish.
According to a first aspect of the invention, a presser foot system for sewing machine, comprising: a pair of presser feet disposed before a needle location to allow for flexible contact with a throat plate; a knife trimming mechanism disposed in the course of a fabric guide path formed between the opposed surfaces of the presser feet, with which the upper edges of the ends of fabrics in a vertical face-to-face contact to be fed to the fabric guide path are cut to an even length by using sliding contact in a horizontal plane between a fixed knife and a movable knife; and upper and lower guides with which movement of the end of one of the fabrics cut to the even length by the knife trimming mechanism and movement of the end of the other are guided respectively to stack one on another on the stitch plate, wherein, the distance from the center of the needle location to a cutting starting position of the knife trimming mechanism is set to a sufficient value so that the ends of the fabrics cut to the even length by one operation of the knife trimming mechanism are stacked one on another until these reach the needle location.
According to a second aspect of the invention, the presser foot system for sewing machine according to the first aspect is characterized in that the distance from the center of the needle location to the cutting starting position of the knife trimming mechanism is set to the range of 16.5 mm to 18.0 mm.
With the first or second aspect, the edges of the fabrics cut to an even length in their vertical position can be brought down completely until these reach the needle location and then fed to the needle location in a predetermined stacked state, even when the cutting width for each operation of the knife trimming mechanism varies depending on the thickness and flexibility of the fabric material, and when the height from the upper surface of the stitch plate to the cutting position varies somewhat due to difference in altitude of the setting position of the fixed knife and movable knife in the knife trimming mechanism inherent in each sewing machine, and further, when a thick stage is present at the initiation and termination of sewing. Therefore, such a poor finish that a projected portion toward a seam direction is formed at a location of the initiation and termination of sewing can be prevented to permit a sewing article exhibiting high quality finish over the entire length.
In the presser foot system for sewing machine according to the first or second aspect, as a means for setting the distance from the center of the needle location to the cutting starting position of the knife trimming mechanism, it can be considered to shift a knife trimming mechanism having the same cutting width as the conventional one to the reverse direction of the sewing direction. In this case, however, the upper and lower guides to guide movement of the ends of fabrics cut to an even length should be improved as a whole in the guide start position and the amount of overhang toward the fabric guide path. This results in a complicated structure.
According to a third or fourth aspect of the invention, there is provided a means for increasing the cutting width of the movable knife and fixed knife in the knife trimming mechanism. This case requires no improvement of the upper and lower guides, resulting in a simple structure.
According to a fifth aspect of the invention, the means for increasing the cutting width of the movable knife and fixed knife in the knife trimming mechanism is one selected from the group consisting of: a means for increasing the ratio of the width of the blade part to the width of the sliding contact guide piece in the movable knife; a means for increasing the entire width of the movable knife while the ratio of the width of the blade part to the width of the sliding contact guide piece in the movable knife is held constant; and a means for increasing the entire width of the movable knife and increasing the width of the blade part to the width of the sliding contact guide piece.
According to a sixth aspect of the invention, a presser foot system for sewing machine, comprising: a pair of presser feet disposed before a needle location to allow for flexible contact with a throat plate; a knife trimming mechanism disposed in the course of a fabric guide path formed between the opposed surfaces of the presser feet, with which the upper edges of the ends of fabrics in a vertical face-to-face contact to be fed to the fabric guide path are cut to an even length by using sliding contact in a horizontal plane between a fixed knife and a movable knife; and upper and lower guides with which movement of the end of one of the fabrics cut to the even length by the knife trimming mechanism and movement of the end of the other are guided respectively to stack one on another on the stitch plate, wherein, a cutting edge of a blade part of the movable knife or fixed knife in the knife trimming mechanism is corrugated and a cutting edge of the corresponding fixed knife or movable knife is formed linearly.
With the construction of the sixth aspect, since the movable knife or fixed knife of the knife trimming mechanism has the corrugated cutting edge, its cutting quality is superior to that of the linear cutting edge, and the function of cutting at a predetermined cutting width is ensured even for very thick fabrics, without causing remainder. That is, the cutting width obtained by one operation of the knife trimming mechanism (indicated by xe2x80x9cCWxe2x80x9d in FIG. 12) is stabilized, and the ends of the fabrics cut to an even length can be brought down completely until these reach the needle location and then fed in a predetermined stacked state to the needle location. Therefore, even for very thick fabrics, it is able to prevent such a poor finish that a projected portion toward a seam direction is formed at a location of the initiation and termination of sewing. This ensures a sewing article that exhibits high quality finish over the entire length.
According to a seventh or eighth aspect of the invention, the presser foot system for sewing machine according to the sixth aspect is characterized by using hard metal or ceramics for the movable or fixed knife of which cutting edge is corrugated.
With this construction, the anti-wear characteristics and durability of the knife having the corrugated cutting edge can be increased, and the knife trimming mechanism can maintain excellent cutting quality as a whole for a long period of time, by polishing only the other knife having the linear cutting edge.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.